How about a "--onlyupdates" type argument for emerge? There are a number of programs I choose not to install (or I just plain uninstalled them) that are part of the "world/system" specification, so when I do "emerge --pretend --update system world" it spits out a few packages I don't want to install, along with the updated packages I DO want to install.

This is where the --onlyupdates argument could be of use: emerge --pretend --update world system --onlyupdates would spit out only packages that are updates. emerge --update --onlyupdates world system would install all packages that are updates (and only updates) to my system.

Because --update includes things I DON'T want to install! For example, if I unmerge raidtools (part of the world/system package), then do
'emerge --update world', the system will install raidtools (because it's part of the world package) even though I dont want it on my computer. An --onlyupdates option would allow me to only update software which is already installed on the computer -- ie, only programs with a "U" before them will be show up if I did emerge --pretend --onlyupdates world.